1. Field of the Invention
The invention generally relates to the field of protection devices. In particular, the invention is a solid-state disconnect device capable of preventing the flow of undesirable voltage or current transients and/or isolating equipment from undesirably high voltages or currents.
2. Background
Traditional protection devices which function as circuit disconnects, examples including fuses and electromechanical circuit breakers, are inherently problematic. For example, such devices have low-switching speeds, require replacement after each trip event, are prone to arcing and switching bounce with associated noise and wear problems, and/or are often large on a volume basis resulting in an unwieldy package.
Solid-state technology applied to such protection devices avoids these disadvantages while offering higher reliability and longer lifetime. Accordingly, solid-state circuit disconnects have become desirable alternatives to traditional protection devices.
Various solid-state disconnect devices have been devised utilizing complex circuitry with an additional power source, examples including devices by Billings et al. in U.S. Pat. No. 4,245,184 entitled AC Solid-State Circuit Breaker, Witmer in U.S. Pat. No. 5,606,482 entitled Solid State Circuit Breaker, Partridge in U.S. Pat. No. 6,104,106 entitled Solid State Circuit Breaker, and Covi et al. in U.S. Pat. No. 6,515,840 entitled Solid State Circuit Breaker with Current Overshoot Protection. However, it is more desirable that a circuit protection device includes two terminals and no additional power source, much like a fuse.
Harris, in U.S. Pat. No. 5,742,463 entitled Protection Device using Field Effect Transistors, describes a two-terminal, solid-state protection device without an additional power supply. Several disadvantages are noteworthy. First, the protection device requires p-channel, high-voltage field-effect-transistors (FETs) which generally have a high conduction resistance because of low hole mobility. Second, the protection device requires both gate-to-source terminals and gate-to-drain terminals of the FETs to have the same high-voltage blocking capability which is difficult to achieve because FETs block the voltage between the drain-to-source and drain-to-gate terminals, and the gate-to-source terminal generally does not have such blocking capability. For example, the gate and source terminals of all known FETs typically block a few volts to a few tens of volts because of a low-voltage Schottky barrier diode in MESFETs, a low-voltage PN diode in JFETs, and a low-voltage MOS capacitor in MOSFETs. Third, the protection device requires a large number of FETs connected in series to increase the voltage blocking capability of the device, inevitably resulting in a higher conduction loss. Fourth, the tripping current is difficult to control with the protection device.
Therefore, what is required is a solid-state disconnect device having two terminals and no additional power supply that avoids the disadvantages of the related arts.